This invention relates to a mining auger used in particular for the underground mining of coal. The auger has a hollow shaft and at least one helix attached to the outer cylindrical face of the shaft. The helix carries, along its outer edge, a plurality of spaced cutting tool bits.
Single-helix or multi-helix augers for the underground mining of coal are known in which separate spray nozzles are associated with the individual cutting tool bits in order to cause settling of rock and coal dust generated during the operation of the auger. As a rule, the nozzles are so oriented that each cutting bit is exposed to one part of the jet approximately in the upper third of the free bit length. As a result, the tool bits are simultaneously cooled which lengthens their service life. The water is admitted to the nozzles--which are arranged in the auger helix--through the auger shaft. From the shaft the water enters into a distributor channel which is arranged in the foot zone of the respective helix and in the frontal end ring of the auger. It is further conventional to arrange the distributor channel directly in the foot zone of the end ring and orient it in the circumferential direction thereof. Or, the distributor channel is located centrally in the foot zone of the respective helix (the foot zone is in contact with the outer face of the auger shaft). In the latter case, the distributor channel has a course which corresponds to that of the helix and extends in the direction of the outer face of the hollow auger shaft. The openings of the individual nozzles are connected with the distributor channel by means of radially extending connecting channels in the end ring and in the helix. In the known structures the connecting channels are provided by deep-drilling.
It was found that connecting channels which are constituted by deep-drilled bores involve substantial manufacturing disadvantages. They have to be made with special deep-drilling machines which involves substantial manufacturing costs. It is a particularly significant disadvantage that such distributor channels are always arranged close to the outer surface of the auger shaft. Thus, these channels are located in a zone on which forces generated during the operation of the auger act with a particularly large lever arm. Since both the helix and the end ring are connected to the shaft by welds, these forces have their effect precisely in a zone which is critical concerning the liquidtight properties of the distributor channels. It was found in practice that the distributor channels often loose these properties during operation, because the forces acting on the hollow auger shaft through large lever arms frequently cause hairline ruptures which, after a short time, lead to substantial leaks of the distributor channels. An additional difficulty in practice was found to be the fact that the helices have to be bent or pressed into a relatively complicated spiral configuration. Similarly, the foot zones which have to be welded to the outer face of the auger shaft have also such a complex shape. In practice, however, it has been found impossible to bend or press the foot zones in an ideal manner to ensure that the walls of the distributor channel lie squarely on all upper surface zones of the auger shaft. Such a positioning, however, is a precondition for a tight welding. On the contrary, it was found in practice that at several locations of the foot zones, unavoidable gas of greater or lesser dimensions appear which are caused by the inherent inaccuracies in the manufacture during bending or pressing of the helices. If now subsequently the foot zone is welded to the auger shaft, weld beads will penetrate into the distributor channel leading, after a short time, to significant corrosions within the channel system. As a result, the nozzles, whose openings often have a diameter of only one millimeter or less, are partially or entirely clogged by the corrosion-caused deposits after a relatively short service life, so that the dual function of the nozzle (namely dust precipitation and a cooling of the hard metal tool bits) can no longer be performed. A further consequence is an overall unsatisfactory operation of the mining auger which thus, after a short period of time, has to be disassembled, moved above ground and repaired in a circumstantial manner, for example, by drilling out the throat welds of the helix and then repairing the same by rewelding.